1. Field of the Invention
The present invention relates to a seal structure, and more particularly to an improved metal seal structure useful for fluid flow controlling devices such as butterfly valves operating in environments where high temperature excursions may cause failure of the primary heat-destructible sealing element or where high temperature fluids or fluids containing abrasive materials are being controlled.
2. Description of the Prior Art
A number of prior art patents describe various types of seal structures for butterfly valves. One such patent is U.S. Pat. No. 4,241,895--Sternenberg. The Sternenberg patent discloses a flexible annular metal seal 30 and a rigid retainer ring 36 that cooperates with the metal seal 30 to maintain a lip 30b in fluid-tight contact with a circumferential sealing surface 28 of a fluid control disc 26. The Sternenberg valve seal has an arcuate-shaped cross-section resembling a quarter of a torus, with one edge of the torus held in a position against a radial surface of the valve body by a retainer ring with the seal mounted as a cantilever. When the flow control element is closed it presses against the curved portion of the torus and moves the free edge of the torus against the surface of the retainer ring until the seal operates in the structural span mode. The Sternenberg seal operates in the cantilever mode as the flow control element is being closed, and operates in the structural span mode after the flow control element is closed. (See col. 2, lines 4-11)
Another prior art patent which discloses a device for effecting a seal is U.S. Pat. No. 4,220,172--Stager. In the Stager patent a seal is effected between a seating surface 41 of metal seating ring 36 and a sealing surface 32 of a valve disc 13. Interference between terminal edge 42 of seating ring 36 and ramps 43 and 44 formed in the wall of the passageway preloads seating surface 41 against sealing surface 32.
Other patents which disclose devices having lips for effecting a seal in cooperation with a disc member include: U.S. Pat. No. 4,175,578--Priese (lip portion 48 forms a seal in cooperation with a valve disc or element 26); U.S. Pat. No. 4,130,285--Whitaker (cantilever sleeve 84 having a sealing surface 86 forms a seal in cooperation with a disc 16); U.S. Pat. No. 3,986,699--Wucik, Jr. et al. (lip 28 forms a seal in cooperation with sealing surface 13 of valve disc 12); U.S. Pat. No. 4,231,546--Eggleston et al. (sealing portion 30 forms a seal in cooperation with surface 15 of closure member 14); and U.S. Pat. No. 3,834,663--Donnelly (lip 50 having a surface 52 forms a seal in cooperation with peripheral sealing edge 22 of disc 20). In addition, the Stager patent, the Priese patent, the Whitaker patent, and the Wucik patent disclose the combination of a lip type of secondary seal and a resilient, heat destructible primary seal member.
U.S. Pat. No. 4,266,752--Johnson discloses a seal structure utilizing a resilient annular ring contained within an annular cavity, which annular ring has a tongue which abuts against the valve disc to effect a seal. One embodiment of the present invention combines a primary, heat destructible seal ring of the type described in the Johnson patent with a metal seal ring to provide a second, metal-to-metal seal which allows the valve to continue to function in the event the primary seal fails, for example due to high temperatures. The metal seal has a unique configuration which both enhances its sealing effectiveness and cooperates with the cavity to maintain the primary seal in proper position for optimum performance. In another embodiment of the present invention, the metal seal is used without any primary, heat destructible sealing means of the type described in the Johnson patent.